Process of making red lead



Feb. 26, 1935. c. c. ROSE El AL PROCESS OF MAKING RED LEAD Filed Aug //Ws/vroes: CZAkE/VCECIPOSi P/c/mea 55: 5

ATTORNEYS- Patented Feb. 26, 1935 UNITED STATES rnocEss or, MAKING mn Lmm Clarence 0. Rose and Richard E. Sears, Cleveland, Ohio, assignors to Willard Storage Battery Company, Cleveland, Ohio, a corporation of West Virginia Application August 6, 1931, Serial No. 555,434

r 3 Claims.

certain uses such as for making paste for storage battery plates.

A further object is to provide a processby which red lead may be produced in continuous fashion and automatically in the sense that the material which is to be treated and oxidized to red lead is introduced preferably by a substantially continuous feeding operation at one end of i a suitable retort and the finished, product in very finely divided form is substantially continuously removed from, the opposite end without requiring anyhand manipulation or even any attention on the part of the operator at any point in the cycle of operation or course of treatment.

A still further object is to provide a process such that the reaction in the conversion of the raw material to red lead may be carried out at substantially atmospheric pressure with air and not an otherwise enriched gaseous mixture.

The above and other objects are attained by the present invention, which may be here briefly summarized as consisting in the steps of the novel process which will bemore fully described 9 below, the invention having special utility in connection with certain raw. materials which or a portion of which are in a continuous fashion converted to red lead, after a conversion to an oxide of lower order. I

In. the accompanying sheet of drawing, we have shown conveniently or diagrammatically a retort which maybe used to advantagein carrying out the process, the single figure being a vertical sectional view. I

, Inour improved process, the material operated on is oxidized to red lead by subjecting it to any oxidizing medium, preferably air, in the presence of heat (both the retort and theairitself being preferably heated) andto substantially continu= ous agitation, preferably by rotating, the retort and therefore cascading the material, being treated as, it passes slowly from the inlet end to the outlet end of the retort. Specific conditions ofheat, rate of rotation, length of the, retort, and therefore thetime .of treatment, will vary with the particularmaterial being treated. The material whichwe prefer to employ we term, gray oxide; consistingof a finely powdered mixture of metallic lead andan oxide, (lower than red lead), the; mix reavine an. women.v ontent. (by

weight) from approximately 3.58% to approxi mately, 4.66% and does not spontaneously ignite in the air.

The gray oxide is preferably obtained by tum-- blinglead balls or pieces of lead in a rotating, container under oxidizing conditions so that as the, oxide is formed, it, as well as particles of the lead, will be ground ofi. The apparatus and the process utilized for obtaining the gray oxide in the manner just stated are preferably similar to the apparatus and process disclosed in U. S. Letters Patent No. 1,675,345, granted July 8, 1928, to Clarence A. Hall, wherethe oxidation is continued far enough to produce a product which does not spontaneously ignite in the air.

While the precise characteristics of the gray oxide, i. e., percentage of oxide, apparent density, etc., may bevaried, and while no specific or definite characteristics of the kinds mentioned are essential to our invention, we prefer to use gray oxide, the color of which may be generallydescribed as greenish gray, with anlapparent density varying between 28 and 35 gramsper cubic, inch with, anoxygen content in excess. of 3.58%

by weight, and, of a fineness such that the major portion of the material will pass through a standard 250mesh screen. Excellent results are ob-, tained by us by using gray oxide having an oxygen content of approximately 4.66% by weight and with an apparent density of 32.5 grams per, cubic inch, and a true specific gravity of approximately, 9.97, the fineness of this, material being such that approximately10% to 12% will be re-, tained on a standard 250 mesh screen, and approximately 5% to 7% will be retained on a300- meshscreen used seriallywith respect to the first mentioned screen. Gray oxide having these 9 characteristics can be very readily produced by the apparatus and process described in said Patent.No,, 1,6 75,345. We might add that the degree of oxidation as well as the fineness of the gray oxide, afiects easeof oxidation to red lead as. well .asthe apparent, density and fineness of the latter,

The -Pbs04 content of the finished product will depend to, some extent upon the characteristics of the raw material used as well as upon the particulate rawmaterial employed and to some ex-' tentupon the controllable-factors of the process, such as the temperature employed, amount of air, rate of rotation, and time of oxidation. It is understood that what is termed red lead need not and generally does not have aPbaOi content of 100% With ourprocess it is quite feasible to bbjail l red; lead, from gray oxide. or the other raw materials mentioned having a Pb30 i content up to approximately 90%, but for storage battery use we endeavor to and do actually obtain red lead having a PbsOi content of between and 75%, the balance being principally PbO; but with the same raw materials, by varying the time of treatment; the temperature, the amount of air supplied, and such conditions, the P131504 content can be varied considerably from that just mentioned.

produced by our process preferably in a retort 10 which may be of cylindrical form as illuss trated, and is supported to rotate on a horizontal or substantially horizontal axis by means of wheels 11 which or part of which may be used for rotating the retort. This retort is made from alloys which will maintain their strength at the elevated temperatures employed and will not oxidize as a result of any decomposition of red lead and the attendant evolution of oxygen. The retort is preferably surrounded, for at least a portion of its length, with insulation 12 which may or may not be attached to the retort so as to rotate therewith. When the raw material beingtreated consists of or contains metallic lead such as gray oxide described above, the insulation preferably does not extend the full length of the retort, as indicated in the drawing, but is omitted from a portion of the retort at its inlet end. This is for the purpose of preventing the temperature rising too high at this end of the retort since the oxidation to PhD in exothermic in its action, the heat of the reaction is high, andma'y require dissipation and. therefore the cooling of. the retort by allowing it to come in contact'with the air at room temperature is desired at or adjacent to the inlet endwhere the major portion of the oxidation of the finely divided metallic lead of the gray oxide to litharge occurs. Means for positively cooling this end of the retort may be desired, as, for example, by use of an air blast. I

The raw material which is indicated at 13 is,

in this instance, supplied from a hopper 14 and outlet end to the inlet end. The delivery chute has an outlet pipe 18601 the withdrawal of air just beyond the opening 17. This pipe of course may be connected to a suitable dust collector, if

necessary.

The constant feeding of the fine material into the inlet end ofthe retort and the rotation of the latter cause the material in the retort to gradually move toward the outlet end and to pass out through the centrally arranged outlet opening 19. This passage of material lengthwise is brought about Without requiring any positive feeding but occurs by the natural tendency of the material to seek its level. This is the case even though the retort is rotated on a horizontal axis, but it may be aided by tilting the retort though the tilting is not necessary. The rate of rotation of the retortis such thatthe material will be carried up along the side of the retort and then dropped down or cascaded so to speak so as to obtain the maximum oxidizing eifect. The fact that the raw 'm'ate'rial'is introduced into the retort near the center of the inlet end and that the finished product passes out near the center of the outlet end thereof, provides a substantial depth of charge in the retort and this condition enhances the cascading effect. The red lead which passes out through the opening 19 drops into a suitable delivery pipe or chute 20.

The-retort is heated for a portion of its length and for this purpose electric heaters, indicated Jet 21, may be employed but other means of heat- Referring now to the drawingtheredlead is ing maybe utilized. When gray oxide having the characteristics above described is employed,

. the heating elements preferably surround the retort for aboutorle-half or two-thirds of its length, i. e., from'the outlet end to or beyond the middle. This portion of the retort is maintained by the heating elements 21 at the best reaction temperature, which is approximately 850 F. at which the conversion from litharge to red lead takes place. However, the temperature may be varied from this temperature, in both directions, without affecting the process, but, if so, changes in the temperature from that just stated should. be accompanied by corresponding changes in the,

rate or air flow, speed of rotation of the retort,

or the rate of feed of the raw material, to produce the desired results. The temperature may varied from approximately 800 F. to approximately 900 F. without materially affecting the results, but the temperature should not be below the reaction temperature of redlead, nor too high to break up the red lead or sinter it. Likewise, at the inlet end where the temperature is considerably lower, as, for example, at a suitable point between room temperature and 400 F., there may also be some variation in the temperature, depending upon the materials used. The desirable temperature is one wherein the finely divided metallic lead is oxidized to litharge rapidly but yet not fast enough either to fuse the lead or sinter the litharge which is produced directly from the metallic lead. It might be added that by controlling the temperature from the outlet end where the red leadis delivered to the inlet end where the raw material'is supplied, sintering at all points in the cycle of operations can be avoided and the final product need not be ground but remains in a finely divided condition suitable for whatever uses it may be put to, as, for example, in making plates of storage batteries. t will be noted that the insulation and the heating elements, when arranged as illustrated, constitute. a heatingfurnace for the retort, and. in this connection it might be stated that any other suitable furnace, such as a gas fired furnace, may be utilized. 7

The oxidation of the litharge to red lead and of the metallic lead to litharge is brought about at a sufiiciently rapid rate to enable the apparatus to be operated with a high degree of efficiency by supplying heated air to the retort by way of the outlet opening 19 so that it will pass countercurrent to the flow of the material in the retort and be delivered out by way'of the inlet opening 17 to the air outlet pipe 18. For this purpose we may employ an air supply pipe 22 which may surround the tubular outlet opening 19,'as illustrated. This air is heated preferably by electric heating elementsindicated at '23, as this method of heatingallows an accurate temperaturecontrol. The air'is supplied at a temperature which is preferably the same as the temperatureat which the retort is maintained at its outlet end by thejheating element 21 (or other means) as it is not intended that the heated plied by the heating means.

is supplied in suiiicient volume to furnish the air either add to or subtract from the heat sup- Of course the air necessary oxygen for the oxidizing steps of the process plus the necessary excess of oxygen to exceed the decomposition pressure of Pb304.

I It will be understood, of course, that while our process works satisfactorily with the use of air as the oxidizing medium, any other available suitable oxidizing gas or mixture may be employed. However, other means for heating the air may be employed, as by a countercurrent of air next to the retort in a spiral coil or equivalent device.

In operation, the raw material 13 is supplied from the hopper and fed continuously to the rotating retort which, as explained above, is heated at least at its outlet end and is supplied with a suitable volume of heated air which passes through the retort contrariwise to the general direction of flow of raw material from the hopper. The rotation of the retort causes a constant agitation or cascading with a gradual feed toward the outlet end, with the result that the material is, by the action of the heat and the oxidizing medium, together with the agitation, converted to red lead which passes substantially continuously through the outlet opening 19. This continuous feeding of the raw material and the continuous formation of red lead are believed to be novel when the raw material consists of a,

mixture of metallic lead and an oxide below red lead. However, the process is particularly novel,

important and effective when the raw material is gray oxide, especially the fine gray oxide produced in the manner and having substantially the characteristics mentioned above in describing the preferred raw material. In this event, the conversion of the fine metallic lead to litharge takes place before the material reaches the zone heated for conversion to red lead and then, before the material reaches the outlet, the conversion to red lead takes place. This result is obtained without disturbing the fine powdered condition of the material. That is to say, the red lead has substantially the fineness of the fine gray oxide as is desired for storage batteries and possibly other uses. A further advantage of this fineness in the gray oxide lies in the fact that it greatly facilitates the conversion to red lead since the surface of each particle exposed to the oxidizing action of the air is practically the maximum.

Having thus described our invention, we claim:

1. The process of making red lead from a material in the form of a finely divided powder composed in part of metallic lead and largely of an oxide of lead lower than red lead, which coma prises passing the material lengthwise through a single continuous heated rotating retort so that the material will be cascaded and thus agitated, passing an oxidizing medium through the retort, and maintaining the temperature in the retort at the outlet end thereof and for a distance toward the inlet end at a relatively high temperature suitable for the formation of red lead and at the same time maintaining adjacent the inlet end of a lower temperature suitable for the conversion of the metallic lead of the powder to litharge without fusion of the lead.

2. The process of making red lead from a finely divided material consisting of gray oxide substantially as described, which comprises passing the material lengthwise through a single continuous heated rotating retort so that the material will be cascaded and thus agitated, passing an oxidizing medium through the retort, and maintaining the temperature in the retort at the outlet end thereof and for a distance toward the inlet end at a relatively high temperature suitable for the formation of red lead and at the same time maintaining adjacent the inlet end a lower temperature suitable for the conversion of the metallic lead of the powder tolitharge without fusion of the lead.

3. The process of making red lead from a material in the form of a finely divided powder composed in part of metallic lead and largely of i an oxide of lead lower than red lead, which'comprises passing the powder lengthwise through a single continuous retort, causing the powder as it passes from one end of the retort to the other to be agitated, passing an oxidizing medium through the retort, heating the retort and maintaining within the retort at the outlet end and for a distance lengthwise thereof toward the inlet end a temperature high enough for the formation of red lead and at the same time maintaining adjacent the inlet end a lower temperature suitable for the conversion of the metallic lead of the powder to litharge without fusion of the lead.

CLARENCE c. ROSE, RICHARD E. SEARS. 

